Owing to their self-leveling property, SL compositions are often used for the purposes of saving the labor and improving the efficiency involved in the operation of surface finish on concrete structures. They have gained rapid widespread use to replace the conventional mortar or concrete direct finish, mainly as the under-floor plaster-work-finish in buildings or the continuous foundation top leveler in houses. The SL compositions for use in these under-floor working and other methods include gypsum and cement based compositions.
There are included some SL compositions having a minimal change with time of fluidity and a fast setting time as the present invention aims. They are designed so as to control the relevant properties by the type and amount of water-reducing agent, the addition of a setting retarder, a combination of a setting accelerator with a setting retarder, or the like.
With respect to the cement-based SL compositions, JP-A 10-231165 discloses to adjust the pot life using a lithium salt as the setting accelerator and aluminum sulfate as the setting retarder at the same time. In this composition, the lithium salt such as lithium carbonate serves as the setting accelerator to alumina cement, and the aluminum sulfate has a set retardation effect to alumina cement, indicating the combined use of setting retarder and setting accelerator to the overall system. They have positive and negative effects on the pot life, respectively, so that the pot life may be controlled. However, since the resultant effect is largely governed by a proportion of two additives, it is difficult to meet both the pot life and the setting time.
JP-A 63-74945 relates to a method of adding cellulose ether to concrete or mortar. Post addition of a slurry of cellulose ether is disclosed therein. The water-soluble cellulose ether must be pre-treated with glyoxal and an acid such as an aliphatic carboxylic acid before it is dispersed and dissolved.
With respect to gypsum-based SL compositions, JP-A 55-56057 discloses to use type II anhydrous gypsum in combination with a setting accelerator such as potash alum and a setting retarder such as borax. Although the setting retarder is concomitantly used in order to establish a pot life, it is difficult to meet both contradictory parameters, pot life and setting time by adjusting the amounts of setting accelerator and retarder added.
For tile attachment, on the other hand, wet and dry methods are known. The wet method includes use of organic adhesives as well as ordinary cement-based mortar for tile attachment. The dry method includes retention by fixtures or the like. Of these, the cement-based mortar is most often used for tile attachment because of low cost, stable effect and durability. For the mortar for tile attachment, not only adhesion, but also the open time during which tiles can be attached (that is, pot life) are of significance. Additionally, a mortar having a short setting time is required to meet the current demand for more efficient working.
As the tile adhesive mortar having a long open time, for example, JP-A 2000-203915 discloses to add a combination of water-soluble cellulose ethers having different setting delay times in order to increase the open time. If a water-soluble cellulose ether having a long setting delay time is used alone, an open time is established, but the setting time is undesirably prolonged. The patent thus proposes to use it along with a water-soluble cellulose ether having a short setting delay time in order to control the setting time. This combination ensures a long open time, but the setting time is slowed, raising a problem against quick working.
JP-A 2000-103662 discloses an aqueous solution of surface-treated water-soluble cellulose ether having a viscosity at 35° C. which is limited to a certain range for preventing the aqueous solution from reducing its viscosity in summer or at high temperatures. Tile adhesive mortar using this aqueous solution, however, is not expected to have a longer open time and a shorter setting time. In JP-A 2000-128617, an open time is ensured using a water-soluble cellulose ether having a relatively long set retardation time and an algal water-soluble polymer having set retardation effect in combination. This method provides a noticeable set retardation effect and a long open time, but has the drawback of a long setting time.
Accordingly, there is a desire to have a tile adhesive mortar having a long open time (or long pot life) and a short setting time.